This invention relates generally to devices for punching holes or like openings in paper, among other materials, and particularly to hand-operated punching devices or punches such as that incorporated with a portable stapler to provide an integrated device capable of both perforating and stapling operations. More particularly, this invention deals with a punch element of improved configuration for use in such hand-operated punching devices wherein the punch element is required to follow an arcuate path in moving into and out of mating engagement with a die.
A conventional punch element for hand-operated punching devices of the type under consideration has had its cutting or perforating end concaved so as to provide a pair of diametrically opposed, arcuate cutting teeth. These teeth have rounded crests and rounded roots. The punch element of this known configuration is the same as those used in the usual tabletop punching machines designed exclusively for perforating paper or the like.
With such tabletop punching machines the prior art punch elements are capable of properly piercing desired material, even extremely thin and pliant paper. This is because the punching machines permit precisely linear motion of the punch elements into and out of the die holes, affording a close running fit between punch elements and dies.
A problem occurs, however, when the prior art punch element finds its way into, for example, a punching device incorporated with a portable stapler. In the punch-stapler combination the punch element is carried by the staple magazine, and the corresponding die by the base, as disclosed for example in my U.S. Pat. No. 3,951,325. The staple magazine and the base are pin-jointed, each at one end, for pivotal motion toward and away from each other.
This construction of the punch-stapler combination compels the punch element to follow an arcuate path, centering at the pivot of the staple magazine, in its travel into and out of the hole in the die. The die hole must therefore receive the punch element with some clearance. If minimized by the critical positioning of the pivot, this clearance does not affect the ability of the punch-stapler combination to perforate usual letter paper or the like. Yet the device may be unable to properly perforate extremely thin paper or paper of some special texture.